Blood sample analyzers for analyzing blood samples collected from humans and animals are known.
The blood cell analyzers aspirate a blood sample from a sample container that holds a blood sample, prepare a measurement sample from the aspirated blood sample and reagent, and measure the measurement sample in a measurement section to obtain measurement results.
Japanese Laid-Open Patent Publication No. 2006/292732 discloses a blood cell analyzer capable of measuring the number of red blood cells, number of white blood cells, and hemoglobin. This blood cell analyzer is preloaded with a liquid in the aspirating tube, and is configured to aspirate a blood sample into the aspirating tube with an air gap (layer of air) formed at the tip of the aspirating tube. The blood sample aspirated into the aspirating tube is slightly diluted by the residual liquid remaining on the inner wall of the aspirating tube in conjunction with the movement within the tube despite contact being prevented between the blood sample and the liquid within the aspirating tube by the air gap. Hence, the concentration of the blood sample disposed at the base end side of the aspirating tube is slightly lower compared to the concentration of the blood sample disposed at the tip end side of the aspirating tube, and a slight concentration gradient is produced in the blood sample within the aspirating tube.
U.S. Patent Application Publication No. 2010/248293 discloses a blood cell analyzer capable of performing classification measurements of white blood cells, measurement of reticulocytes, and measurement of nucleated red blood cells in addition to measurements of the number of red blood cells, number of white blood cells, and hemoglobin. This blood cell analyzer is configured to obtain measurement order of specified measurement items, calculate the amount of blood sample needed for the measurement according to the measurement item specified in the measurement order, aspirate the calculated amount of blood sample from the sample container, and execute the measurements of each measurement item.
The blood cell analyzer disclosed in Japanese Laid-Open Patent Publication No. 2006/292732 is configured to measure each sample for predetermined measurement items and aspirate a fixed amount of blood sample into the aspirating tube for each measurement, therefore sample aspiration conditions for each measurement is identical. Therefore, the concentration gradient of the blood sample within the aspirating tube, for example, is the same for each measurement. In this blood cell analyzer, blood samples diluted to the same degree are used in identical measurement items for any measurement since which part of a blood sample in the aspirating tube to use for a measurement item is determined beforehand. The measurement results are therefore unaffected by the concentration gradient produced in the blood sample within the aspirating tube.
On the other hand, when the blood cell analyzer disclosed in Japanese Laid-Open Patent Publication No. 2006/292732 is configured to change the type and number of measurement items for each sample similar to the blood cell analyzer of U.S. Patent Application Publication No. 2010/248293, it is necessary to aspirate an amount of sample capable of supporting all measurement items even when, for example, only measuring a single measurement item since a fixed amount of blood sample must be aspirated whatever measurement is to be performed in order to have identical aspiration conditions for each sample (blood sample).
When the blood cell analyzer disclosed in Japanese Laid-Open Patent Publication No. 2006/292732 is configured to change the type and number of measurement items for each sample, there is concern of some fluctuation in the concentration gradient of the sample within the aspirating tube for each sample due to the difference in the amount of aspirated sample in each measurement when only the required amount of sample needed for the measurement is aspirated, as in the case of the blood cell analyzer of US Patent Application Publication No. 2010/248293. Therefore, when an equal part of the sample of the aspirating tube is used in identical measurement items for each measurement, there will be a slight difference in the degree of dilution of the sample in each measurement, which causes concern that the measurement results will be affected.
Note that washing liquid remains on the inner wall of the aspirating tube and sampling valve because the aspirating tube and the sampling valve are washed each measurement even when aspirating a blood sample that does not fill the interior of the aspirating tube as in blood analyzers that measure blood samples using the sampling valve. There is therefore concern of some variation of the blood sample concentration gradient among measurements when different amounts of sample are aspirated for each measurement. Common measurement items are preferably performed under identical sample aspiration conditions for each measurement.